Solid solution approach for redox active metal organic frameworks with tunable redox conductivity

ABSTRACT

Various embodiments relate to a method for producing a metal-organic framework (MOF) having a desired redox conductivity and including redox-active linkers, having w-alkyl-ferrocene groups, via de novo solvothermal synthesis. Various embodiments relate to a metal-organic framework (MOF) linker comprising an w-alkyl-ferrocene group. Various embodiments relate to a metal-organic framework (MOF), having a first plurality of redox-active linkers, each having an ω-alkyl-ferrocene group. The MOF according to various embodiments, may further have one or more redox-inactive linkers. Various embodiments relate to materials, apparatuses, and components that include the MOF according to various embodiments. For example, various embodiments relate to thin-films, bulk powders, or electrodes.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/913,470, filed Oct. 10, 2019, titled A SOLID SOLUTIONAPPROACH FOR REDOX ACTIVE METAL ORGANIC FRAMEWORKS WITH TUNABLE REDOXCONDUCTIVITY, which is incorporated by reference herein in its entirety.

BACKGROUND

There is a need for systematically tuning the conductivity ofmetal-organic frameworks (MOFs) to achieve desired combinations ofporosity and electrochemical attributes. The discussion of shortcomingsand needs existing in the field prior to the present invention is in noway an admission that such shortcomings and needs were recognized bythose skilled in the art prior to the present disclosure.

BRIEF SUMMARY

Various embodiments relate to a method for producing a metal-organicframework (MOF) having a desired redox conductivity and comprisingredox-active linkers, each having ω-alkyl-ferrocene groups, the methodcomprising: performing a de novo solvothermal synthesis of the MOF,using the redox-active linkers and redox-inactive linkers in a ratiosufficient to provide the MOF with the desired redox conductivity. TheMOF so-produced may, according to various embodiments, display a maximumelectron conductivity of about 122 mS cm⁻¹, and/or crystallographic andelectrochemical stability upon a number of redox cycles greater than1,000.

Various embodiments relate to a metal-organic framework (MOF) linkercomprising an ω-alkyl-ferrocene group. For example, the metal-organicframework (MOF) linker according to various embodiments, may have astructure according to Formula I:

wherein R may be an alkyl of any suitable size and configuration, suchas, for example, a C₁ to C₂₄ alkyl. The R group may be branched, cyclic,linear, or a combination thereof.

Various embodiments relate to a metal-organic framework (MOF),comprising a first plurality of redox-active linkers, each having anω-alkyl-ferrocene group. The MOF according to various embodiments, mayfurther comprise one or more redox-inactive linkers. For example,according to various embodiments, the MOF may comprise a repeating unithaving a composition according to Formula II:

Zr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆  (II),

wherein Fc represents the plurality of redox-active linkers, wherein NRrepresents the one or more redox-inactive linkers, and wherein x is from2 to 100. According to various embodiments, the MOF may displays amaximum electron conductivity of about 122 mS cm⁻¹, and/orcrystallographic and electrochemical stability upon a number of redoxcycles greater than 1,000.

Various embodiments relate to materials, apparatuses, and componentsthat comprise the MOF according to various embodiments. For example,various embodiments relate to a thin-film comprising the MOF, a bulkpowder comprising the MOF, or an electrode comprising the MOF.

These and other features, aspects, and advantages of various embodimentswill become better understood with reference to the followingdescription, figures, and claims.

BRIEF DESCRIPTION OF THE FIGURES

Many aspects of this disclosure can be better understood with referenceto the following figures.

FIG. 1A is an example according to various embodiments, illustrating aschematic depiction of a MOF thin film electrode containing variedamounts of redox active links that enable fast re-dox conductivity viaredox hopping.

FIG. 1B is an solution amounts of redox active links. example accordingto various embodiments, illustrating a synthesis of MOF thin filmelectrodes with a finely tuned substitutional solid.

FIG. 2A is an example according to various embodiments illustrating aplot of the SSS input-output mol % ratio of the Fc link incorporated inthe thin film MOFs as determined by EDXS evidencing 1:1 input-outpouincorporation.

FIG. 2B is an example according to various embodiments illustrating GIXDof MOF thin films grown on FTO substrates, in which stars denote peakscorresponding to FTO.

FIG. 3A is an example according to various embodiments illustratingcyclic voltammetry data of Fc containing MOF electrodes, specifically,cyclic voltammograms at various Fc link content (scan rate of 20 mV s−1,in 0.1 M LiBF4 in MeCN and Pt counter electrode).

FIG. 3B is an example according to various embodiments illustratingcyclic voltammetry data of Fc containing MOF electrodes, specifically,peak current of the 100% Fc MOF electrode as a func-tion of the squareroot of scan rate.

FIG. 3C is an example according to various embodiments illustratingcyclic voltammetry data of Fc containing MOF electrodes, specifically,peak currents of the MOF electrodes as a function of their ferrocenecontent (scan rate of 20 mV s−1).

FIG. 4A is an example according to various embodiments illustratingUV-visible absorption spectra of 100 mol % Fc MOF thin film before(orange trace) and after oxidation (blue trace), evidencing theformation of ferricenium ion.

FIG. 4B is an example according to various embodiments illustratingAb-sorbance of ferricenium as a function of Fc content in the MOF thinfilms.

FIG. 4C is an example according to various embodiments illustratingdiffusion coefficient of electron transfer derived from Anson plots asfunction of Fc content (orange symbols), compared to modeled De fromEqs. (1) and (2) (blue line).

FIG. 4D is an example according to various embodiments illustratingtunable electron conductivity of the MOF electrodes at varied Fc content(orange symbols) derived from Einstein-Stokes equation compared to model(blue line).

FIG. 5 is an example according to various embodiments illustratingstacked ₁H NMR from MOF decomposition in DMSO-d₆.

FIG. 6A is an example according to various embodiments illustrating anSEM image of 0% Fc powder.

FIG. 6B is an example according to various embodiments illustrating a Zrmapping overlay of the SEM image of the 0% Fc powder referenced in FIG.6A.

FIG. 7A is an example according to various embodiments illustrating anSEM image of 50% Fc powder.

FIG. 7B is an example according to various embodiments illustrating a Zrmapping overlay of the SEM image of the 50% Fc powder referenced in FIG.7A.

FIG. 7C is an example according to various embodiments illustrating a Femapping overlay of the SEM image of the 50% Fc powder referenced in FIG.7A.

FIG. 7D is an example according to various embodiments illustrating a Zrand Fe mapping overlay of the SEM image of the 50% Fc powder referencedin FIG. 7A.

FIG. 8A is an example according to various embodiments illustrating anSEM image of 100% Fc powder.

FIG. 8B is an example according to various embodiments illustrating a Zrmapping overlay of the SEM image of the 100% Fc powder referenced inFIG. 8A.

FIG. 8C is an example according to various embodiments illustrating a Femapping overlay of the SEM image of the 100% Fc powder referenced inFIG. 8A.

FIG. 8D is an example according to various embodiments illustrating Zrand Fe mapping overlay of the SEM image of the 100% Fc powder referencedin FIG. 8A.

FIGS. 9A, 9B, 9C, and 9D are examples according to various embodimentsillustrating square root scan rate dependence of peak current for40-100% Fc samples.

FIGS. 10A, 10B, and 10C are examples according to various embodimentsillustrating scan rate dependence voltammograms of 100% Fc, 20% Fc, and10% Fc, respectively (scan rate: 20 mV s⁻¹).

FIG. 11 is an example according to various embodiments illustrating animage of a charged/oxidized Fc thin film.

FIGS. 12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12I, 12J, 12K, and 12L areexamples according to various embodiments illustrating anson plots forFc MOFs for both charging (anodic) and discharging (cathodic) steps.

FIGS. 13A, 13B, 13C, and 13D are examples according to variousembodiments illustrating UV-vis spectra of charged and uncharged FcMOFs. Zoomed portions of the spectra near 630 nm appear in the insets.

FIG. 14 is an example according to various embodiments illustratingAbsorbance trend at 630 nm of the coverage/thickness-corrected chargefilms.

FIGS. 15A, 15B, 15C, 15D, 15E, and 15 F are examples according tovarious embodiments illustrating overlaid simulated and experimentalcyclic voltammograms of Fc MOFs.

FIG. 16 is an example according to various embodiments illustratingDiffusion coefficients of Fc MOFs determined by Anson plots, simulation,and redox polymer theory.

FIG. 17A is an example according to various embodiments illustratingOptical image of 10% Fc thin film.

FIG. 17B is an example according to various embodiments illustratingOptical image of 20% Fc thin film.

FIG. 17C is an example according to various embodiments illustratingOptical image of 40% Fc thin film.

FIG. 17D is an example according to various embodiments illustratingOptical image of 60% Fc thin film.

FIG. 17E is an example according to various embodiments illustratingOptical image of 80% Fc thin film.

FIG. 17F is an example according to various embodiments illustratingOptical image of 100% Fc thin film.

FIG. 18A is an example according to various embodiments illustrating 50%Fc nitrogen adsorption isotherm at 77 K.

FIG. 18B is an example according to various embodiments illustrating 50%Fc in a Rouquerol plot.

FIG. 18C is an example according to various embodiments illustrating 50%Fc in a BET plot.

FIG. 19A is an example according to various embodiments illustrating100% Fc nitrogen adsorption isotherm at 77 K.

FIG. 19B is an example according to various embodiments illustrating aRouquerol plot of a 100% Fc sample.

FIG. 19C is an example according to various embodiments illustrating aBET plot of a 100% Fc sample.

FIG. 20 is an example according to various embodiments illustratingLinear isotherms of three solid-solutions exhibiting the mesopore tomicropore transition in the inset.

FIG. 21 is an example according to various embodiments illustrating Poresize distributions of Fc MOFs.

FIG. 22 is an example according to various embodiments illustrating 50%Fc water adsorption isotherm.

FIG. 23 is an example according to various embodiments illustrating 100%Fc water adsorption isotherm.

FIG. 24A is an example according to various embodiments illustrating aPXRD of Fc MOFs having the formula Zr₆O₄(OH)₄[(Fc)₀(NR)₁]₆ before andafter water adsorption isotherms.

FIG. 24B is an example according to various embodiments illustrating aPXRD of Fc MOFs having the formula Zr₆O₄(OH)₄[(Fc)_(0.5)(NR)_(0.5)]₆before and after water adsorption isotherms.

FIG. 24C is an example according to various embodiments illustrating aPXRD of Fc MOFs having the formula Zr₆O₄(OH)₄[(Fc)₁(NR)₀]₆ before andafter water adsorption isotherms.

FIG. 25 is an example according to various embodiments illustrating 100%Fc MOF voltammogram in 0.1 M sulfuric acid medium run for 1500 cycles(scan rate: 50 mV s⁻¹).

FIG. 26 is an example according to various embodiments illustrating 100%Fc PXRD before (bottom) and after (top) 1500 0.1 M sulfuric acid mediumelectrochemical cycles (*=FTO).

FIGS. 27A, 27B, 27C, 27D, 27E, 27F, and 27G are examples according tovarious embodiments illustrating TGA of Fc MOFs.

FIG. 28 is an example according to various embodiments illustrating FTIRof Fc MOFs.

It should be understood that the various embodiments are not limited tothe examples illustrated in the figures.

DETAILED DESCRIPTION Introduction and Definitions

This disclosure is written to describe the invention to a person havingordinary skill in the art, who will understand that this disclosure isnot limited to the specific examples or embodiments described. Theexamples and embodiments are single instances of the invention whichwill make a much larger scope apparent to the person having ordinaryskill in the art. Unless defined otherwise, all technical and scientificterms used herein have the same meaning as commonly understood by theperson having ordinary skill in the art. It is also to be understoodthat the terminology used herein is for the purpose of describingexamples and embodiments only, and is not intended to be limiting, sincethe scope of the present disclosure will be limited only by the appendedclaims.

All the features disclosed in this specification (including anyaccompanying claims, abstract, and drawings) may be replaced byalternative features serving the same, equivalent, or similar purpose,unless expressly stated otherwise. Thus, unless expressly statedotherwise, each feature disclosed is one example only of a genericseries of equivalent or similar features. The examples and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to theperson having ordinary skill in the art and are to be included withinthe spirit and purview of this application. Many variations andmodifications may be made to the embodiments of the disclosure withoutdeparting substantially from the spirit and principles of thedisclosure. All such modifications and variations are intended to beincluded herein within the scope of this disclosure. For example, unlessotherwise indicated, the present disclosure is not limited to particularmaterials, reagents, reaction materials, manufacturing processes, or thelike, as such can vary. It is also to be understood that the terminologyused herein is for purposes of describing particular embodiments onlyand is not intended to be limiting. It is also possible in the presentdisclosure that steps can be executed in different sequence where thisis logically possible.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (for example, having the same functionor result). In many instances, the term “about” may include numbers thatare rounded to the nearest significant figure.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a support” includes a plurality of supports. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

As used herein, the term “standard temperature and pressure” generallyrefers to 25° C. and 1 atmosphere. Standard temperature and pressure mayalso be referred to as “ambient conditions.” Unless indicated otherwise,parts are by weight, temperature is in ° C., and pressure is at or nearatmospheric. The terms “elevated temperatures” or “high-temperatures”generally refer to temperatures of at least 100° C.

Unless otherwise specified, all percentages indicating the amount of acomponent in a composition represent a percent by weight of thecomponent based on the total weight of the composition. The term “molpercent” or “mole percent” generally refers to the percentage that themoles of a particular component are of the total moles that are in amixture. The sum of the mole fractions for each component in a solutionis equal to 1.

Ferrocene is an organometallic compound with the formula Fe(C₅H₅)₂ andthe structure:

The molecule consists of two cyclopentadienyl rings bound on oppositesides of a central iron atom.

An alkyl substituent is an alkane missing one hydrogen. The term alkylis intentionally unspecific to include many possible substitutions. Anacyclic alkyl has the general formula of C_(n)H_(2n+1). A is derivedfrom a cycloalkane by removal of a hydrogen atom from a ring and has thegeneral formula C_(n)H_(2n−1). Typically an alkyl is a part of a largermolecule. In structural formula, the symbol R is used to designate ageneric (unspecified) alkyl group. The smallest alkyl group is methyl,with the formula CH₃—.

Greek letters α, β, γ, and so on, may be used to designate successivepositions along a hydrocarbon chain. The carbon directly attached to theprincipal function group is denoted as α, the second carbon is β, and soon down the chain. The omega (ω) position is sometimes used to designatethe last position along the chain regardless of its length. Thus, forexample, ω-bromohexanoic acid is 6-bromohexanoic acid. An“ω-alkyl-ferrocene” as used herein refers to a molecule of the followingstructure:

in which “R” represents an alkyl group. The alkyl group may be alinear,branched, or cyclic, and may have any number of carbon atoms. Forexample, the alkyl group may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or more carbon atoms.

As used herein, “ω-alkyl-ferrocene group” refers to a moiety, which maybe pendant to or part of a molecule, as illustrated by the followingstructure:

in which “R” represents an alkyl group. “X” represents any chemicalstructure to which the moiety may be covalently bonded. In other words,an “ω-alkyl-ferrocene group” refers to any “ω-alkyl-ferrocene” moleculethat has been covalently bonded to another molecule via some part of itsalkyl group. According to various embodiment described herein, the “X”structure may be a metal-organic framework (MOF).

As used herein, “metal-organic framework” or “MOF” refers to a class ofcompounds consisting of metal ions or clusters coordinated to organicligands to form one-, two-, or three-dimensional structures. They are asubclass of coordination polymers, with the special feature that theyare often porous. A metal-organic framework is a coordination networkwith organic ligands containing potential voids. A coordination networkis a coordination compound extending, through repeating coordinationentities, in one dimension, but with cross-links between two or moreindividual chains, loops, or spiro-links, or a coordination compoundextending through repeating coordination entities in two or threedimensions; and finally a coordination polymer is a coordinationcompound with repeating coordination entities extending in one, two, orthree dimensions. MOFs are composed of two major components: a metal ionor cluster of metal ions and an organic molecule called a “linker.”

Various embodiments described herein relate to a “linker” for ametal-organic framework or a “MOF linker.” More specifically, variousembodiments relate to an MOF linker that comprises an ω-alkyl-ferrocenegroup. Other embodiments relate to MOFs prepared from or comprising theMOF linkers having ω-alkyl-ferrocene groups. Again, the MOF linkers arethe organic portion of an MOF that also comprises at least one metalion. Various embodiments relate to products, systems, or apparatusesthat comprise the MOF, such as, for example, an electrode.

Reticular Chemistry is concerned with the linking of discrete molecularbuilding units into crystalline porous extended structures throughstrong bonds. As used herein, a “reticular material” refers generally toa material produced via Reticular Chemistry, such as, for example amaterial comprising a metal-organic framework (MOF) and/or a covalentorganic framework (COF).

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit (unlessthe context clearly dictates otherwise), between the upper and lowerlimit of that range, and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present disclosure is not entitled to antedate suchpublication by prior disclosure. Further, the dates of publicationprovided could be different from the actual publication dates that mayneed to be independently confirmed.

General Discussion

Systematically tuning the conductivity of metal-organic frameworks(MOFs) is key to synergizing their attractive synthetic control andporosity with electrochemical attributes useful in energy and sensingtechnologies. A priori control of electron conductivity is possible byexploiting the solid-solution properties of MOFs together withelectronic self-exchange enabled by redox pendants. Various embodimentsdescribed herein relate to a new strategy for preparing redox-active MOFthin film electrodes with finely tuned redox pendant content. Varyingthe ratios of alkyl-ferrocene containing redox-active and inactive linksduring MOF synthesis enabled the fabrication of electrodes with tunableredox conductivity. The prepared MOF electrodes, according to variousembodiments, may display maximum electron conductivity of 122 mS cm⁻¹,and crystallographic and electrochemical stability upon thousands ofredox cycles. Electroanalytical studies demonstrated that theconductivity follows solution-like, diffusion-controlled behavior withnon-linear electron diffusion coefficients consistent withcharge-hopping and percolation models with spatially fixed redoxcenters. Various embodiments provide new prospects in the design andsynthesis of redox-active MOFs with targeted properties for the designof advanced electrochemical devices.

Understanding charge transport in reticular materials like metal-organicframeworks (MOFs) creates opportunities for advanced device design inphotovoltaics, energy storage, electrocatalysts, and electrochemicalsensors. Of the many strategies proposed to impose conductivity in MOFs,covalent incorporation of redox active mediators (RAMs) into otherwisedielectric MOFs offers the advantage of high modularity via synthesis,enabling systematic composition-property relationship studies. Thisstrategy takes advantage of a diversity of available RAMs which displaywide ranges of redox potentials and electron transfer kinetics. In thismanner, charge transport in MOFs through the use of attached RAMs isattributed to electron “hopping” mediated by self-exchange reactionsthat result in diffusion of electrons within the MOF, creating anelectric current. By incorporating RAMs with known fast self-exchangekinetics, it is possible to predesign MOFs that exhibit high redox-basedconductivity. Several strategies have been explored to incorporate RAMsinto MOFs, such as: non-covalent impregnation of guest RAMs in thepores, using RAMs in single-linker MOFs, and via post-synthetic covalenttethering of RAMs at the defect sites of the MOF. Various embodimentspresent a new strategy for tuning the redox conductivity of multivariateMOFs using the concept of substitutional solid solution (SSS) strategy,by incorporating varied amounts of links containing covalently boundRAMs that display fast electron exchange kinetics.

FIG. 1A is an example according to various embodiments, illustrating aschematic depiction of a MOF thin film electrode containing variedamounts of redox active links that enable fast redox conductivity viaredox hopping. For this purpose, development of various embodimentsinvolved anchoring ω-alkyl-ferrocene groups in the organic links of thezirconia based PEPEP-PIZOF-2 MOF, and preparing MOF SSS thin-filmelectrodes to observe how the electron hopping between alkyl-ferrocenechanges with varied ferrocene content. This was achieved by simplyvarying the ratios of redox-active and inactive links such as Fc and NR(Fc=alkyl-ferrocene containing link and NR=non-redox active link, FIG.1B), respectively, leading to observable changes in redox conductivitythat resemble electrochemical behavior in solution. FIG. 1B is anexample according to various embodiments, illustrating a synthesis ofMOF thin film electrodes with finely tunes substitutional solid solutionamounts of redox active links.

Cyclic voltammetry (CV) and potential-controlled chronocoulometry (CC)showed that the conductivity is diffusion controlled and is completelydependent on the Fc link content. Since the ferrocene RAMs arecovalently attached to the MOF, their long-range mobility is restricted,thus the diffusion-controlled conductivity arises solely from electronexchange between ferrocene pendants. The prepared MOF thin-filmelectrodes display the expected spectroelectrochemical response from theferricenium/ferrocene pair. Subjection of the MOF films to over 1,000 CVcycles in aqueous acidic electrolyte (0.1 M H₂SO₄) demonstrate theirchemical and structural stability during the electrochemical experimentand observed clear retention of both their crystal structure and redoxactivity. Thus, the MOF-based SSS platform presented here offerscontrollable modulation of electron conductivity along with excellentstability, making it an ideal candidate for both fundamental chargetransport studies and MOF-based devices.

Thin films of MOFs with formula Zr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆ containingvaried SSS x input amounts of redox active and inactive linkers weregrown onto fluorine-doped tin oxide (FTO) substrates via solvothermalsynthesis in N,N-dimethylformamide (DMF) with ZrOCl₂ and benzoic acidfor 14 h at 110° C. (FIG. 1B). Treating the clean FTO substrates byimmersing them in a Fc solution for 24 h before solvothermal growthensured the formation of films with complete coverage and thicknessesbetween 5-7 μm, as determined by optical profilometry. Scanning electronmicroscopy coupled with electron dispersive X-ray spectroscopy(SEM/EDXS) analysis of the films showed homogeneous distribution ofoctahedrally shaped crystallites with homogeneously dispersed Fethroughout the film. The Zr/Fe ratio measured from EDXS displayed a near1:1 input/output incorporation of Fc links in the matrix.

FIG. 2A is an example according to various embodiments, illustrating aplot of the SSS input-output mol % ratio of the Fc link incorporated inthe thin film MOFs as determined by EDXS evidencing 1:1 input-outputincorporation. FIG. 2B is an example according to various embodiments,illustrating GIXD of MOF thin films grown on FTO substrates, in whichstars denote peaks corresponding to FTO. Powder X-ray diffraction ingrazing incidence mode (GIXD, FIG. 2b ) showed that the films are highlycrystalline and isotropic and exhibit sharp diffraction lines that wereassigned to the MOF and FTO. High intensity peaks at low angle (4.08°2-theta, CuKa) confirmed the formation of the Fd-3m cubic phase ofPIZOF-2 matrix throughout the series. The thin-film growing media alsoproduced bulk powders that, after base digestion and ¹H NMR spectroscopyanalysis, exhibited same linker incorporation ratio as in the thinfilms. The bulk powders exhibit high porosity, with N₂ adsorptionuptakes and Brunauer-Emmett-Teller (BET) surface areas consistent withincreased alkyl-ferrocene loading between 1860-1048 m² g⁻¹.Interestingly, increasing Fc content also results in change in isothermtype from mesoporous in x=0 mol %, to microporous in x=100 mol % asresult of pore filling by the alkyl-ferrocene pendants. The MOF powdersare also stable to humidity, retaining their crystallinity and BETsurface area even after H₂O vapor adsorption cycles at 300 K.

Cyclic voltammetry of the prepared MOF thin-film electrodes isreminiscent of a redox system undergoing linear diffusion. FIG. 3A is anexample according to various embodiments, illustrating cyclicvoltammetry data of Fc containing MOF electrodes, specifically, cyclicvoltammograms at various Fc link content (scan rate of 20 mV s−1, in 0.1M LiBF4 in MeCN and Pt counter electrode). In contrast to asurface-confined redox species with instantaneously accessible RAMs,which displays symmetrical Gaussian-shaped peaks and a linear dependenceof peak current with scan rate, the MOFs according to variousembodiments display peak splitting and a square dependence on scan rate,characteristic of diffusive systems. FIG. 3B is an example according tovarious embodiments, illustrating cyclic voltammetry data of Fccontaining MOF electrodes, specifically, peak current of the 100% Fc MOFelectrode as a function of the square root of scan rate. The larger peaksplitting observed in these CVs compared to an ideal diffusive system,i.e., 57 mV for a one-electron exchange, is ascribed to be the sum ofresistances derived from the non-metallic character of the film. Afundamental difference between the behaviors of ferrocene dissolved inZr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆ MOFs and a freely diffusing redox species inliquid solution is that the redox centers in the former are spatiallyfixed, restricting the charge diffusion mechanism to electron hoppingbetween neighboring RAM sites. This condition allows for strongmodulation of electron transport properties by means of redox centerloading, which in this case is controlled a priori by the input ratiosof Fc/NR linkers. FIG. 3C is an example according to variousembodiments, illustrating cyclic voltammetry data of Fc containing MOFelectrodes, specifically, peak currents of the MOF electrodes as afunction of their ferrocene content (scan rate of 20 mV s−1). FIG. 3cshows the effects of Fc loading in the Zr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆ filmson voltammetric peak currents displaying non-linear trends, in strongcontrast to the linear dependence of peak current versus concentrationin freely diffusive redox systems. This trend of reduced electroactivityfor dilute ferrocene MOFs also manifested in their UV-visible absorptionspectra. After 15 min of oxidative charging, films with high Fc contentdisplay a clear absorbance peak near 630 nm (FIG. 3a inset), indicatinga change from ferrocene to ferricenium ion. This absorbance peakcoincides with a visible color change in the more concentrated filmsfrom orange-yellow (ferrocene) to bluish-green (ferricenium, FIG. S3).FIG. 3a displays a plot of absorbance versus x (mol % Fc content) thatmatches the voltammetric peak trend, where more dilute samples displayeda lower electrochemical accessibility in the 15 min timeframe.

Changes in redox hopping dynamics resulting from redox center dilutionwere probed by evaluating the diffusion coefficient of charge transfer(D_(e)). In this system, the tunneling distance for electron hoppingbetween sites was expected to be higher for more dilute samples, causingD_(e) values to lower with decreasing Fc loading. To test thishypothesis, diffusion coefficients of oxidative and reductive chargingin the film were measured through chronocoulometry by subsequentoxidizing and reducing potential steps. Anson plots, which graph chargecollected versus square root of time, were used to extract diffusioncoefficients that have concentration dependence similar to thevoltammetric peak currents. Various embodiments may use a modeldeveloped for redox-active polymeric films to predict theoreticaldiffusion coefficients of charge transfer as a function of concentration(FIG. 3b ). This model derives diffusion coefficients in redox pendantnetworks from charge transfer dynamics via the Dahms-Ruff expressionwith restricted physical diffusion of redox species (Eq. 1), and theexchange kinetics expression (Eq. 2):

D _(e)=1/6k _(et) r _(NN) ²  (1)

k _(et) =k′e ^(−r) ^(NN) ^(−r) ^(o) ^()/δ)  (2)

where k_(et) is the electron self-exchange rate constant, and r_(NN) isthe average distance between nearest neighboring pendants, k′ is theintrinsic facility of charge transfer between pendants, δ is acharacteristic length representing electronic coupling strength in themedium, and r₀ is the contact radius of the pendant. The model predictsthat D_(e) increases exponentially at low concentrations, eventuallybecoming roughly linear. Values for k′ and δ were found by fitting thetheoretical curve to the experimental data points. The k′ valueobtained, 1.2×10⁷ s⁻¹, is one order of magnitude larger than the rateobserved on ferrocene anchored to a metal electrode (k′=1.6×10⁶ s⁻¹).The δ value, 1.1 Å, is similar to the analogous distance dependenceconstant for electron transfer through saturated alkane chains.

The prediction that high pendant-pendant distance at low concentrationscauses sluggish charge diffusion aligns with percolation theory, whichapplies to the conductivity of networks in which the nodes are a randomdistribution of conductors (pendants) and insulators (unmodifiedlinkers). Percolation theory predicts that there is some critical ratioof conductors in a given network below which the network ceases toeffectively conduct. Indeed, the critical ratios for 3D networks relatedto the MOF (isotropic cubic lattice with 6-12 nearest neighbors) are inthe range of 20-30%, similar to the Fc content percentages in MOFs abovewhich large increases in peak currents and UV-visible absorption areobserved. The redox conductivity of the MOFs was obtained from theEinstein-Stokes equation for charged diffusive systems resulting incomposition-dependent redox conductivity with a maximum conductivity ofσ_(e)=122 mS cm⁻¹ in the 100% Fc MOF (FIG. 4d ), comparable to theintrinsic electron conductivity of undoped germanium.

FIG. 4A is an example according to various embodiments, illustratingUV-visible absorption spectra of 100 mol % Fc MOF thin film before(orange trace) and after oxidation (blue trace), evidencing theformation of ferricenium ion. FIG. 4B is an example according to variousembodiments, illustrating Ab-sorbance of ferricenium as a function of Fccontent in the MOF thin films. FIG. 4C is an example according tovarious embodiments, illustrating diffusion coefficient of electrontransfer derived from Anson plots as function of Fc content (orangesymbols), compared to modeled De from Eqs. (1) and (2) (blue line). FIG.4D is an example according to various embodiments, illustrating tunableelectron conductivity of the MOF electrodes at varied Fc content (orangesymbols) derived from Einstein-Stokes equation compared to model (blueline).

The structural and electrochemical stability of the prepared films wasprobed by exposing the 100 mol % Fc MOF electrode to multiple CVcharge-discharge cycles in 0.1 M H₂SO₄(aq). After 1400 cycles, the onlyobservable change in the voltammogram is a slight shift in peak currentover time, related to improved wetting of the electrolyte over time.GIDX of the cycled film showed very little changes in diffractionpattern, evidencing retention of the MOF architecture. Variousembodiments provide a new metal-organic framework design withcapabilities for fine-tuning of redox pendant concentration. Thistunability was exploited to study the effect of redox pendantconcentration on electroactivity. Results imply there is a set ofparameters that determine electrochemical accessibility inredox-modified MOG films: pendant RAM concentration and self-exchangekinetics.

Examples Introduction

The following examples are put forth to provide those of ordinary skillin the art with a complete disclosure and description of how to performthe methods, how to make, and how to use the compositions and compoundsdisclosed and claimed herein. Efforts have been made to ensure accuracywith respect to numbers (e.g., amounts, temperature, etc.), but someerrors and deviations should be accounted for. The purpose of thefollowing examples is not to limit the scope of the various embodiments,but merely to provide examples illustrating specific embodiments.

Materials and Methods

All starting materials and solvents, unless otherwise specified, wereobtained from commercial sources (Aldrich, Fisher, VWR) and used withoutfurther purification. Anhydrous tetrahydrofuran (THF),N,N-dimethlyformamide (DMF), and CH₂Cl₂ were purified using acustombuilt alumina column based solvent purification system (InnovativeTechnology). Deuterated solvents CDCl₃ and DMSO-d₆ were obtained fromCambridge Isotope Labs.

High-resolution ₁H, and ₁₃C, nuclear magnetic resonance (NMR) spectrawere collected using a Bruker AVANCE-III 400 MHz spectrometer. ₁H and₁₃C chemical shifts are referenced to TMS as 0 ppm and assigned usingthe residual solvent signal. NMR data processing was performed usingMestReNova version 10.0.2-15465. High resolution mass spectra (HRMS)were recorded using an Agilent 6230 TOF coupled with an Agilent ZorbaxSB-C18 analytical column. Column chromatography was performed using aTeledyne Isco Combiflash Rf₊. Infrared spectroscopy was performed with aJasco FT/IR-6600. Thermogravimetric analysis was performed with aShimadzu TGA-50H from 25° C. to 800° C. with a ramp speed of 5° C.min⁻¹.

Powder X-ray diffraction (PXRD) measurements were performed using aRigaku Miniflex 600 diffractometer, with θ−2θ Bragg-Brentano geometry,and a 600 W (40 kV, 15 mA) Cu X-ray tube source using Kα (λ=1.5418 Å)radiation, samples were measures from 4 to 60 2θ-degrees with a stepsize of 0.02° and a scan rate of 1.5 s per step. Samples were preparedby dropping the powder sample in a silicon zero background sample holderand pressing the powder gently with a clean glass slide. Thin-filmgrazing incidence X-ray diffraction (GIXD) were performed using aPANanalytical Empyrean diffractometer in grazing incidence mode withθ−2θ Bragg-Brentano geometry, and a 1.8 kW (40 kV, 45 mA) Cu X-ray tubesource using Kα radiation (λ=1.5418 Å), samples were measured from 2 to60 26-degrees with a step size of 0.01671° with a motorized stage with Zand tilt adjustment utilizing X'Celerator multi-element detector. Filmthickness measurements and optical images were acquired using a KeyenceVK-X1000 3D Laser Scanning Confocal Microscope. Film and powdercomposition analysis was performed using a Zeiss ULTRA-55 SEM equippedwith a Noran System 7 EDXS system with a Silicon Drift Detector xraydetector. UV-vis spectroscopy was performed with an Agilent Cary 5000spectrometer using diffuse transmittance mode. Voltammetric andchronoamperometric measurements were made with either a CH Instruments760 or 601 potentiostat. N₂ gas adsorption isotherm analysis wasperformed using a Micromeritics ASAP 2020 porosimetry analyzer at 77 K.

NR link was prepared according to published procedures.

Synthetic Procedures

Scheme S1 shows a synthesis according to various embodiments of an MOFlinker (Fc).

3-chloro-1-oxopropyl ferrocene (compound S1): Compound S1 synthesis wasadapted from literature procedures_(s1) from ferrocene. Ferrocene (3.0g, 16.1 mmol, 1 eq) and anhydrous AlCl₃ (2.6 g, 19.4 mmol, 1.2 eq) wereloaded into an oven-dried 100 mL Schlenk flask equipped with a magneticstirbar. The flask was evacuated to an internal pressure of 100 mTorrand backfilled with N₂ three times. Anhydrous CH₂Cl₂ (20 mL) was addedvia syringe under N₂ and stirred at room temperature. 3-Chloropropionylchloride (2.0 g, 16.1 mmol, 1 eq) was added via syringe under N₂ at 0°C. and the reaction was stirred for 5 hours monitored by TLC until thestarting material was no longer observed. The mixture was then pouredinto 1 M HCl (20 mL) below 5° C. and extracted with CH₂Cl₂ (3×20 mL).The combined organic extracts were washed with brine (20 mL) and driedover Na₂SO₄ (anhydrous). The solvent was removed under reduced pressureat 50° C. in a rotary evaporator and the residue was purified via columnchromatography (SiO₂, 1% v/v MeOH/CH₂Cl₂) affording compound S1 as abrown solid. Yield: 74%, 3.3 g. ₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm)4.79 (t, J=2.0 Hz, 2H), 4.53 (t, J=2.0 Hz, 2H), 4.24 (s, 5H), 3.91 (t,J=6.5 Hz, 2H), 3.17 (t, J=6.5 Hz, 2H). ₁₃C NMR (100 MHz, CDCl₃, 25° C.)δ (ppm) 200.47, 78.53, 72.69 (2C), 70.05 (5C), 69.36 (2C), 42.23, 38.93.HRMS (ESI-TOF) m/z: [M]₊ Calculated for C₁₃H₁₃ClFeO 276.0004; Found276.0018.

3-chloro-1-propyl ferrocene (compound S2): Compound S2 synthesis wasadapted from literature procedures_(s1) from S1. Compound S2 (3.0 g,10.8 mmol, 1 eq) was loaded into an ovendried 100 mL Schlenk flaskequipped with a magnetic stirbar. The flask was evacuated to an internalpressure of 100 mTorr and backfilled with N₂ three times. Anhydrous THF(20 mL) was added via syringe under N₂ and stirred at room temperature.Anhydrous AlCl₃ (1.7 g, 13.0 mmol, 1.2 eq) and NaBH₄ (1.2 g, 32.5 mmol,3 eq) were added portion-wise under N₂ at 0° C. The mixture was stirredovernight at room temperature, then poured into 1 M HCl (20 mL) andextracted with CH₂Cl₂ (3×20 mL). The combined organic extracts werewashed with brine (20 mL) and dried over Na₂SO₄ (anhydrous). The solventwas removed under reduced pressure at 50° C. in a rotary evaporator andthe residue was purified via column chromatography (SiO₂, 1% v/vEtOAc/hexanes) affording compound S2 as a yellow oil. Yield: 92%, 2.6 g.₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 4.14 (s, 5H), 4.11-4.08 (m, 4H),3.55 (t, J=6.4 Hz, 2H), 2.49 (t, J=7.5 Hz, 2H), 2.01-1.90 (m, 2H). ₁₃CNMR (100 MHz, CDCl₃, 25° C.) δ (ppm) 87.79, 78.92 (5C), 68.47 (2C),67.67 (2C), 44.84, 33.95, 26.86. HRMS (ESI-TOF) m/z: [M]₊ Calculated forC₁₃H₁₅ClFe 262.0212; Found 262.0214.

4-iodo hexyl benzoate (compound S3): 4-iodo benzoic acid (10 g, 40.3mmol, 1 eq) and K₂CO₃ (16.7 g, 120 mmol, 3 eq) were loaded into anoven-dried 250 mL Schlenk flask equipped with a magnetic stirbar. Theflask was evacuated to an internal pressure of 100 mTorr and backfilledwith N₂ three times. Anhydrous DMF (80 mL) was added via syringe underN₂ and stirred for 20 min at room temperature. 1-bromohexane (18.2 mL,120 mmol, 3 eq) was added via syringe under N₂ and the reaction washeated to 60° C. for 1 h, monitored by TLC until the starting materialwas no longer observed. The reaction was cooled to room temperature,water (50 mL) was added and the crude mixture was extracted using CH₂Cl₂(3×50 mL). The combined organic extracts were then rinsed with water(2×50 mL), brine (50 mL), dried over Na₂SO₄(anhydrous) and filtered. Thesolvent was removed under reduced pressure at 50° C. in a rotaryevaporator and the residue was purified via column chromatography (SiO₂,10% v/v EtOAc/hexanes) affording compound S3 as a colorless oil. Yield:11.9 g, 89%. ₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 7.83-7.78 (d, 2H),7.78-7.73 (d, 2H), 4.31 (t, J=6.7 Hz, 2H), 1.76 (dq, J=8.0, 6.7 Hz, 2H),1.47-1.31 (m, 6H), 0.91 (td, J=5.8, 4.6, 2.8 Hz, 3H). ₁₃C NMR (100 MHz,CDCl₃, 25° C.) δ (ppm) 166.49, 138.02 (2C), 131.34 (2C), 130.39, 100.81,65.74, 31.78, 28.98, 26.01, 22.87, 14.31. HRMS (ESI-TOF) m/z: [M]₊Calculated for C₁₃H₁₇IO₂ 332.0273; Found 332.0284.

4-(2-trimethylsilyl)-ethynyl hexyl benzoate (compound S4): Compound S3(4.0 g, 12.0 mmol, 1 eq), copper(I) iodide (0.14 g, 0.72 mmol), andPd(PPh₃)₂Cl₂ (0.25 g, 0.36 mmol) were added to a 250 mL Schlenk flaskequipped with a magnetic stirbar and a reflux condenser. The flask wasevacuated to an internal pressure of 100 mTorr and backfilled with N₂three times. THF (40 mL) and triethylamine (40 mL) were bubbled for ca.30 min before being added via syringe, followed by trimethylsilylacetylene (2.6 mL, 18.1 mmol). The reaction mixture was then heated to70° C. for 8 h, monitored by TLC until the starting material was nolonger observed. The reaction vessel was cooled to room temperature,water (100 mL) was added, and the resulting solution was extracted withCH₂Cl₂ (3×50 mL). The combined organic phase was washed with 0.5 M HCl(2×50 mL), water (50 mL), brine (50 mL), dried over Na₂SO₄ (anhydrous),and filtered. The solvent was removed under reduced pressure in a rotaryevaporator at 45° C. and the resulting crude was purified via columnchromatography (SiO₂, 5% v/v EtOAc:hexanes) affording compound S4 as abrown oil. Yield: 3.35 g, 92%. ₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm)8.04-7.92 (dd, J=8.3, 2.0 Hz, 2H), 7.58-7.48 (dd, J=8.2, 2.1 Hz, 2H),4.31 (t, J=6.7 Hz, 2H), 1.77 (dt, J=14.4, 6.8 Hz, 2H), 1.48-1.27 (m,6H), 0.97-0.84 (m, 3H), 0.27 (s, 9H). ₁₃C NMR (100 MHz, CDCl₃, 25° C.) δ(ppm) 166.44, 132.18 (2C), 130.43, 129.66 (2C), 127.97, 104.47, 97.91,65.70, 31.8′1, 29.00, 26.04, 22.89, 14.36, 0.20 (3C). HRMS (ESI-TOF)m/z: [M]₊ Calculated for C₁₈H₂₆O₂Si 302.1702; Found 302.1717.

4-ethynyl hexyl benzoate (compound S5): Compound S4 (1.8 g, 6.0 mmol, 1eq) was added to a 150 mL round-bottom flask equipped with a magneticstirbar. Methanol (30 mL) was added and the solution was stirred at roomtemperature for 20 min. Cesium fluoride (2.3 g, 1.2 mmol) was added atroom temperature and the flask was stirred for an additional 2 h,monitored by TLC until the starting material was no longer observed. Thereaction mixture was then poured over 50 mL of ice-water causing theprecipitation of a brown solid. The solid was isolated via filtrationand dried under reduced pressure affording S5 as a brown solid. Yield:1.15 g, 83%. ₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 8.00 (d, J=8.0 Hz,1H), 7.55 (d, J=8.0 Hz, 1H), 4.32 (td, J=6.7, 0.7 Hz, 1H), 1.85-1.68 (m,1H), 1.52-1.22 (m, 3H), 0.97-0.84 (m, 2H). 13C NMR (100 MHz, CDCl₃, 25°C.) δ (ppm) 166.13, 132.18 (2C), 130.69, 129.55 (2C), 126.75, 83.00,80.07, 65.54, 31.60, 28.80, 25.84, 22.69, 14.15. HRMS (ESI-TOF) m/z:[M+H]₊ Calculated for C₁₅H₁₇O₂ 231.1379; Found 231.1380.

2,5-diiodo-4-methoxy phenol (compound S6): Compound S6 was synthesizedaccording to literature procedures₂₉ from 1,4-diiodo-2,5-dimethoxybenzene. Yield 1.5 g, 53%. ₁H NMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 7.42(s, 1H), 7.03 (s, 1H), 4.88 (s, 1H), 3.82 (s, 3H). ₁₃C NMR (101 MHz,CDCl₃) δ 153.46, 150.33, 125.37, 120.06, 87.11, 84.71, 57.55. HRMS(ESI-TOF) m/z: [M]₊ Calculated for C₇H₆I₂O₂ 375.8452; Found 375.8451.

1,4-diiodo-5-methoxy-2-(3-propoxyferrocenyl)-benzene (compound S7):Compound S6 (1.12 g, 3.0 mmol, 1 eq), compound S2 (1.0 g, 3.3 mmol, 1.1eq), and K₂CO₃ (1.3 g, 9.0 mmol, 3 eq) were loaded into a 50 mL Schlenkflask equipped with a magnetic stirbar and reflux condenser. The flaskwas evacuated to an internal pressure of 100 mTorr and backfilled withN₂ gas three times. DMF (6 mL) was added via syringe and the flask washeated to 60° C. for 8 h, monitored by TLC until the starting materialwas no longer observed. The reaction vessel was cooled to roomtemperature and subsequently quenched with water (20 mL) causing theproduct to crash out of solution. The mixture was cooled in an ice-waterbath for 20 min before being filtered. The solid was filtered andair-dried yielding compound S7 as a yellow solid. Yield: 1.5 g, 82%. ₁HNMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 7.22 (s, 1H), 7.18 (s, 1H), 4.14(s, 5H), 4.11 (t, J=1.8 Hz, 2H), 4.07 (t, J=1.8 Hz, 2H), 3.96 (t, J=6.1Hz, 2H), 3.84 (s, 3H), 2.61 (t, J=8.5 Hz, 2H), 2.06-1.99 (m, 2H). ₁₃CNMR (100 MHz, CDCl₃, 25° C.) δ (ppm) 153.65, 153.12, 123.21, 121.84,88.37, 86.65, 85.83, 69.77, 68.94 (5C), 68.55 (2C), 67.64 (2C), 57.54,30.68, 26.28. HRMS (ESI-TOF) m/z: [M]₊ Calculated for C₂₀H₂₀FeI₂O₂601.8902; Found 601.8909.

4,4′-[(2-(3-ferrocenylpropoxy)-5-methoxy-1,4-phenylene)di-2,2-ethynediyl]bis-,1,1′-dihexyl ester benzoic acid (compound S8): Compound S7 (1.68 g, 2.80mmol, 1 eq), compound S5 (1.42 g, 6.20 mmol, 2.2 eq), Pd(PPh₃)₄ (98 mg,0.084 mmol, 0.03 eq), and copper(I) iodide (16 mg, 0.084 mmol, 0.03 eq)were loaded into a 250 mL Schlenk flask equipped with a magnetic stirbarand a reflux condenser. The flask was evacuated to an internal pressureof 100 mTorr and backfilled with N₂ three times. THF (15 mL) andtriethylamine (15 mL) were bubbled for ca. 30 min before being added viasyringe. The flask was heated to 60° C. for 8 h, monitored by TLC untilthe starting material was no longer observed. The reaction vessel wascooled to room temperature, water (40 mL) was added, and the resultingsolution was extracted with CH₂Cl₂ (3×50 mL). The combined organic phasewas washed with 0.5 M HCl (2×50 mL), water (50 mL), brine (50 mL), driedover Na₂SO₄ (anhydrous), and filtered. The solvent was removed underreduced pressure in a rotary evaporator at 45° C. and the resultingcrude was purified via column chromatography (SiO₂, 60% v/vCH₂Cl₂/hexanes) yielding S8 as a yellow solid. Yield: 1.67 g, 76%. ₁HNMR (400 MHz, CDCl₃, 25° C.) δ (ppm) 8.05 (d, J=8.2 Hz, 2H), 8.02 (d,J=8.1 Hz, 2H), 7.64 (d, J=8.1 Hz, 2H), 7.61 (d, J=8.0 Hz, 2H), 7.06 (s,1H), 7.05 (s, 1H), 4.33 (t, J=6.7 Hz, 4H), 4.09 (t, J=1.8 Hz, 2H),4.08-4.02 (m, 9H), 3.93 (s, 3H), 2.64 (t, J=8.5 Hz, 2H), 2.12-2.01 (m,2H), 1.83-1.73 (m, 4H), 1.49-1.31 (m, 12H), 0.96-0.87 (m, 6H). ₁₃C NMR(100 MHz, CDCl₃, 25° C.) δ 166.47, 166.43, 154.42, 154.01, 131.90 (2C),131.79 (2C), 130.38, 130.35, 129.90 (2C), 129.79 (2C), 128.21, 128.06,117.68, 115.64, 114.30, 113.73, 94.87, 94.80, 89.13, 88.81, 88.37,69.04, 68.88 (5C), 68.58 (2C), 67.68 (2C), 65.72 (2C), 56.83, 31.82(2C), 31.00, 29.03 (2C), 26.26, 26.06 (2C), 22.91 (2C), 14.37 (2C). HRMS(ESI-TOF) m/z: [M]₊ Calcd for C₅₀H₅₄FeO₆ 806.3270; Found 806.3265.

4,4′-[(2-(3-ferrocenylpropoxy)-5-methoxy-1,4-phenylene)di-2,2-ethynediyl]bis-benzoicacid (Fc): Compound S8 (1.65 g, 2.1 mmol) was added to a 100 mLround-bottom flask equipped with a magnetic stirbar. THF (15 mL) wasadded and the solution was stirred at room temperature for 20 min beforethe addition of 5 M KOH in methanol (2 mL). The reaction was heated to80° C. for 8 h until the reaction was complete, monitored by TLC untilthe starting material was no longer observed. The reaction mixture wascooled to room temperature and the THF was removed under reducedpressure in a rotary evaporator at 45° C. The resulting crude was thendissolved in water (20 mL) and neutralized with the dropwise addition of2 M HCl until a pH of 3-4 is achieved, causing the formation of a yellowprecipitate. The solid was collected via filtration, washed with water(3×20 mL) and dried under high vacuum yielding Fc link as a yellowsolid. Yield: 1.16 g, 87%. ₁H NMR (400 MHz, DMSO-d₆, 25° C.) δ (ppm)8.00 (d, J=8.8 Hz, 2H), 7.98 (d, J=8.9 Hz, 2H), 7.69 (d, J=8.5 Hz, 2H),7.65 (d, J=8.5 Hz, 2H), 7.26 (s, 1H), 7.25 (s, 1H), 4.11 (t, J=1.7 Hz,2H), 4.07 (t, J=6.0 Hz, 2H), 4.04-4.00 (m, 7H), 3.87 (s, 3H), 2.56 (dd,J=8.9, 6.4 Hz, 2H), 2.02-1.88 (m, 2H). ₁₃C NMR (100 MHz, DMSO-d₆, 25°C.) δ 167.45, 167.43, 154.49, 153.94, 132.22 (2C), 132.14 (2C), 131.39,131.37, 130.41 (2C), 130.37 (2C), 127.57, 127.44, 117.99, 116.13,113.99, 113.37, 94.98, 94.88, 89.62, 89.44, 88.75, 69.08, 69.02 (5C),68.63 (2C), 67.76 (2C), 57.11, 30.69, 26.02. HRMS (ESI-TOF) m/z: [M]₊Calcd for C₃₈H₃₀FeO₆ 638.1392; Found 638.1403.

General Procedure for FTO Substrate Cleaning and Pre-Treatment

The as received FTO glass was cut into 2 cm×1 cm slides, then immersedin an ultrasound bath in soapy water, de-ionized water, acetone, andisopropanol for 20 min each solvent and left to dry in air. In a 20 mLvial, Fc (192 mg, 0.3 mmol) and pyridine (20 μL, 0.3 mmol) weredissolved in anhydrous DMF (15 mL). The clean and dry FTO glass slideswere immersed in the Fc solution for 24 h, rinsed with fresh DMF (2 mL),and air dried.

General Procedure for Zr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆ MOF Synthesis as ThinFilms Over FTO and Bulk Powders

In an Ar-filled glovebox, benzoic acid (330 mg, 2.70 mmol) andZrOCl₂.8H₂O (29 mg, 0.09 mmol) were added to a 20 mL scintillation vialequipped with a magnetic stirbar. DMF (5 mL) was added and the reactionmixture was stirred at 80° C. for 20 min. Mixtures of NR and Fc atvaried mol ratios (0.06 mmol total) were added, and the reaction wasstirred for another 20 min at 80° C. The mixture was then transferred toan 8 mL conical reaction vial containing a pretreated FTO glass slidewith its conductive side facing down. The vial was capped with a glassstopper, removed from the glovebox, and placed in an isothermal ovenheated to 110° C. for 48 h. The vial was removed from the oven andcooled to room temperature for 30 min. The OFcovered FTO slide wasremoved from the reaction vessel, rinsed with fresh DMF, and stored in adesiccator. This procedure also produced the bulk powders, which wereisolated via filtration, rinsed with DMF, CH₂Cl₂, and dried in air andstored in a dessicator.

Table 1 shows stoichiometric linker quantities for solid-statesynthesis. As used herein “x” refers to the “x” in the formulaZr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆ for the MOF according to variousembodiments.

TABLE 1 x (mol % Fc) mmol Fc mmol NR mg Fc mg NR 0 0 0.060 0 25.6 100.006 0.054 3.8 23.0 20 0.012 0.048 7.7 20.5 40 0.024 0.036 15.3 15.4 600.036 0.024 23.0 10.2 80 0.048 0.012 30.6 5.1 100 0.060 0 38.3 0

FIG. 2B provides a PXRD of Fc MOF bulk powders.

NMR and EDXS Composition Analysis

General procedure for MOF digestion and composition analysis via NMR.2.0 mg of MOF powder were placed in a 4 mL vial containing 50 μL of 0.1M NaOD in D₂O, followed by 0.6 mL of DMSO-d₆. The vial was immersed inan ultrasonic bath for 10 min and the digested mixture was transferredto an NMR tube. The tube was left to settle for 24 h. ₁H NMR spectrawere collected with 50 transients at 25° C. The NMR data was processedusing MNova version 9.0.1. The DMSO peak was set to a chemical shift of2.500 ppm. Zero filling was set to 256K, exponential multiplication wasset to 0.15 Hz, baseline correction was done with a Whittaker functionwith manual phase correction. Peak deconvolution was performed in thearomatic region (7.4-7.8 ppm) extracting peak areas at 7.49, 7.44, and7.43 ppm to determine output linker ratios.

General procedure for MOF composition analysis via EDXS. MOF thin filmsand bulk powders were analyzed via SEM-EDXS using a working distance of13 mm and a beam energy of 15 kV with a 60 μm aperture. The atomiccompositions were determined using the iron K lines at 6.4 keV and 7.1keV and the zirconium L lines at 2.0 keV.

FIG. 5 is an example according to various embodiments illustratingstacked ₁H NMR from MOF decomposition in DMSO-d₆. Integration valuesfrom the chemical shifts at 7.49, 7.44, and 7.43 were used to calculatethe output ratios of Fc to NR.

Table 2 shows Fe and Zr concentrations from EDXS analysis.

TABLE 2 Fc content (mol %) Fe (atom %) Zr (atom %) Fe/Zr Ratio 0 0 3.5 ±0.10 0 10 0.2 ± 0.03 1.9 ± 0.09 0.12 ± 0.02 20 0.3 ± 0.03 1.8 ± 0.030.19 ± 0.03 40 0.8 ± 0.01 2.0 ± 0.06 0.40 ± 0.02 60 1.0 ± 0.07 1.8 ±0.10 0.57 ± 0.03 80 1.3 ± 0.03 1.7 ± 0.06 0.79 ± 0.06 100 2.2 ± 0.07 2.2± 0.06 0.98 ± 0.03

EDXS Atom Mapping.

FIGS. 6A and B are examples according to various embodimentsillustrating EDXS of 0% Fc powder. More specifically, FIG. 6A is anexample according to various embodiments illustrating an SEM image of 0%Fc powder; and FIG. 6B is an example according to various embodimentsillustrating a Zr mapping overlay of the SEM image of the 0% Fc powderreferenced in FIG. 6A.

FIGS. 7A, 7B, 7C, and 7D are examples according to various embodimentsillustrating EDXS of 50% Fc powder. More specifically, FIG. 7A is anexample according to various embodiments illustrating an SEM image of50% Fc powder; FIG. 7B is an example according to various embodimentsillustrating a Zr mapping overlay of the SEM image of the 50% Fc powderreferenced in FIG. 7A; FIG. 7C is an example according to variousembodiments illustrating a Fe mapping overlay of the SEM image of the50% Fc powder referenced in FIG. 7A; and FIG. 7D is an example accordingto various embodiments illustrating a Zr and Fe mapping overlay of theSEM image of the 50% Fc powder referenced in FIG. 7A.

FIGS. 8A, 8B, 8C, and 8D are an examples according to variousembodiments illustrating EDXS of 100% Fc powder. More specifically, FIG.8A is an example according to various embodiments illustrating an SEMimage of 100% Fc powder; FIG. 8B is an example according to variousembodiments illustrating a Zr mapping overlay of the SEM image of the100% Fc powder referenced in FIG. 8A; FIG. 8C is an example according tovarious embodiments illustrating a Fe mapping overlay of the SEM imageof the 100% Fc powder referenced in FIG. 8A; and FIG. 8D is an exampleaccording to various embodiments illustrating Zr and Fe mapping overlayof the SEM image of the 100% Fc powder referenced in FIG. 8A.

Electrochemical Methods

For electrochemical analysis, the MOF-coated FTO slides were mountedinto Teflon electrochemical cells. The films would be allowed to soakfor at least six hours in the solvent/electrolyte system (0.1 M LiBF₄ inacetonitrile) before analysis. A platinum counter electrode and a silverquasireference electrode were used, with the MOF-modified FTO as theworking electrode. After analysis, molecular ferrocene was added to thecell and used a 25 μm diameter gold ultramicroelectrode to properlyreference the system.

The charge transport behavior of MOF electrodes was studied via cyclicvoltammetry. The voltammetric peak currents were observed to be afunction of the square root of scan rate, implying diffusive behaviorrather than thin film behavior, which would result in a lineardependence of peak current on scan rate.₃₁ Below in FIG. S6 are theplots of anodic peak current vs the square root of scan rate for the40-100% Fc samples; the cathodic peak heights were harder to accuratelyquantify due to the heavily sloping background of the reductive sweep.The 10% and 20% Fc samples did not have well defined peaks, and thusaccurate peak heights were immeasurable. FIG. S7 shows voltammograms forthe 100% Fc sample at each different scan rate and sample voltammogramsof the 20% and 10% samples showing the lack of welldefined peaks.

FIGS. 9A, 9B, 9C, and 9D are examples according to various embodimentsillustrating square root scan rate dependence of peak current for40-100% Fc samples.

FIGS. 10A, 10B, and 10C are examples according to various embodimentsillustrating scan rate dependence voltammograms of 100% Fc, 20% Fc, and10% Fc, respectively (scan rate: 20 mV s⁻¹).

To both confirm the theoretical concentrations of ferrocene in the MOFsand to measure charge diffusion coefficients, the films were subjectedto highly oxidizing and reducing potential steps, allowingchronocoulometric analysis. The charge vs. square root of time curves(Anson plots) below in FIG. S9 show charge leveling off with time in thehigher concentrated samples (40-100% Fc). This was attributed to bulkdepletion of ferrocene in the films. The more concentrated films havehigher diffusion coefficients, leading to faster bulk electrolysis ofthe films. For the 40-100% Fc films, ferrocene concentrations can beestimated by converting charge electrolyzed at the leveling-off point tomoles of ferrocene via Faraday's law:

Q=nN _(fc) F

where Q is the total charge passed, n is the number of electrons perredox event (one in this case), N_(Fc) is the number of moles offerrocene, and F is Faraday's constant. Moles of ferrocene are thendivided by the volume of film exposed to solution. This volume wasassumed to be a cylinder with height equal to the film thicknessobtained by optical profilometry. The radius of the exposed film areawas measured by observing the films after oxidation, whereupon theygained a bluish tint from the conversion of ferrocene to ferricinium. Apicture of one of the films after oxidation is shown in FIG. S8. Thisarea was larger than the hole in the electrochemical cell, likely due tothe swelling of the cell O-ring and the porosity of the films.

FIG. 11 is an example according to various embodiments illustrating animage of a charged/oxidized Fc thin film. The dark blue circle clearlydisplays the oxidation of ferrocene within the exposed film area.

Table 3 demonstrates how closely the theoretical values of ferroceneconcentration match those obtained experimentally for the 20-100%samples, with the 10% samples only showing 42% of the theoreticalferrocene capacity (Q values for the 10/20% samples were taken as thecharge electrolyzed at the end of the 10 min charging steps). Thisstrongly suggests that the entire thickness of the more concentratedfilms is electrochemically accessible, and not simply the area near theFTO. The striking hue difference between oxidized and unoxidizedportions of the film (along with the UV-vis spectroscopy of the oxidizedfilms) also imply that a significant portion of the film is beingelectrolyzed.

Example Ferrocene Concentration Calculation:

This calculation is for a 100% Fc sample, anodic step. The thickness offilm is 5.4 μm. The approximate radius of exposed area of MOF is 3.5 mm.The thickness of films is given by:

V _(exposed MOF)=5.4×10⁻⁶ m*π*(3.5×10⁻³ m)²=2.08×10⁻¹⁰ m ³=2.08×10⁻⁷ L

The approximate charge reached before leveling of current is 0.025 C.

${0.025\mspace{14mu} C} = {1*N_{Fc}*96485\frac{C}{mol}}$$N_{Fc} = {\frac{0.025\mspace{14mu} C}{96485\frac{C}{mol}} = {2.59 \times 10^{- 7}\mspace{14mu} {moles}\mspace{14mu} {of}\mspace{14mu} {ferrocene}}}$$C_{Fc} = {\frac{2.59 \times 10^{- 7}\mspace{14mu} {mol}}{2.087 \times 10^{- 7}\mspace{14mu} L} = {1.25\mspace{14mu} M}}$

TABLE 3 Fc content [Fc], Theory [Fc], Experiment [Fc]_(exp)/ (mol %) (M)(M) [Fc]_(theory) 100 1.25 1.20 ± 0.15 0.96 80 1.00 0.97 ± 0.17 0.97 600.75 0.74 ± 0.14 0.99 40 0.5 0.42 ± 0.08 0.84 20 0.25 0.27 ± 0.12 1.0810 0.125 0.052 ± 0.018 0.42

In addition to concentration calculations, the Anson plots were alsoused to calculate experimental diffusion coefficients. Both oxidizingand subsequent reducing potential steps were applied to the films,resulting in a current-time curve which follows the Cottrell equation.Integrating the Cottrell equation yields the trend of charge with time:

${Q(t)} = \frac{2{nFAD}^{\frac{1}{2}}C^{*}t^{\frac{1}{2}}}{\pi^{\frac{1}{2}}}$

where n is the number of electrons per charge transfer, F is Faraday'sconstant, A is the area of the electrode, D is the diffusion coefficientof the species being electrolyzed, and C⋅ is the bulk concentration ofredox species. Theoretical concentrations of Fc based off 1.25 M for the100% Fc sample were used (Table S3). Plotting charge vs the square rootof time should yield a straight line. The slope of that line can be usedto calculate the diffusion coefficient of the species of interest, giventhat concentration and the area of the electrode are known. Theseexperiments included both oxidizing steps (corresponding to effectivediffusion of the reduced species) and reductive steps (corresponding toeffective diffusion of the oxidized species). The experimentally deriveddiffusion coefficients are plotted as a function of ferrocene percentagealong with the simulated values from DigiElch software and theoreticalvalues calculated from redox polymer theory in FIG. S12.

Example Diffusion Coefficient Calculation:

This calculation is for 100% Fc, Cathodic Step. Slope of Q vs t1/2 curve(obtained by linear regression; linear portion marked in red in Ansonplots) is 0.0026 C s-1/2

$\mspace{76mu} {{0.0026\frac{C}{s^{\frac{1}{2}}}} = \frac{2{nFAD}^{\frac{1}{2}}C}{\pi^{\frac{1}{2}}}}$$D = {\left( \frac{0.0026\frac{C}{s^{\frac{1}{2}}}*\pi^{\frac{1}{2}}}{2*96485\frac{C}{mol}*3.6 \times 10^{- 5}m^{2}*1250\frac{mol}{m^{3}}} \right)^{2} = {2.8 \times 10^{- 13}\frac{m^{2}}{s}}}$

FIGS. 12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12I, 12J, 12K, and 12L areexamples according to various embodiments illustrating anson plots forFc MOFs for both charging (anodic) and discharging (cathodic) steps.

Films were analyzed with diffuse transmittance UV-vis spectroscopybefore and after 15 minutes of oxidative charging. Visually, the moreconcentrated films turned blue upon oxidation, while the 20% Fc and moredilute samples showed little if any visual change. The intense lightscattering from the films and high background of the base MOF lead tospectra that should be analyzed qualitatively. To correct for differingfilm coverages and thicknesses, the spectra may be divided by theirthickness in microns and multiplied by their surface coverage percentage(both determined by optical profilometry). The raw and correctedspectra, both before and after charging, are shown below in FIG. S10 forall samples.

FIGS. 13A, 13B, 13C, and 13D are examples according to variousembodiments illustrating UV-vis spectra of charged and uncharged FcMOFs. Zoomed portions of the spectra near 630 nm appear in the insets.

FIG. 14 is an example according to various embodiments illustratingAbsorbance trend at 630 nm of the coverage/thickness-corrected chargefilms.

The more concentrated charged films show a clear absorbance peak near630 nm compared to the uncharged spectra. Measuring the absorbancevalues of the coverage/thickness corrected spectra at 630 nm leads to alinear trend. A simple calculation shows that even the slowest diffusingfilms can be fully oxidized within 15 minutes. The following equationpredicts how far a diffusing species travels in a given time:

Δ=√{square root over (2D _(CT) t)}

where Δ is the root-mean-square distance traveled by the diffusingspecies and t is time. Using the diffusion coefficient of the 10% Fc, itis possible to calculate how far the charge can percolate through thefilm within 15 minutes.

Δ=2*6.9×10⁻¹¹ cm²/s*900 s=3.5 μm

Since the films have thicknesses from 3-7 microns, this implies thateven the slowest diffusing films should be able to be charged in 15minutes.

Electrochemical Simulations and Theory

To confirm that the diffusion coefficients obtained from the Ansonanalysis were plausible, voltammograms of the MOFs were simulated withDigiElch (version 7) software. The 20 mV s⁻¹ scans were simulated foreach concentration, and theoretical concentration values were used andwere multiplied by the sample ferrocene ratios; for instance, the 80% Fcsample would have a Fc concentration of 1.25M×0.8. A double capacitanceof 50 μΩ was used for all simulations, and solution resistances obtainedfrom the CHI 760 potentiostat for each sample were inputted to thesoftware (these ranged from 700-1000Ω). A planar geometry was used, withan area of 0.385 cm₂. To simulate the film aspect of the MOFs, finite 1Ddiffusion was used in the simulation using thicknesses determined byoptical profilometry. A closed right boundary condition (BRB in theDigiElch software) was used, which sets the concentration gradient atedge of the film to zero. The voltammograms were fitted by changing thediffusion coefficients of the reduced and oxidized species (filmcharging and discharging, respectively), kinetics of charge transfer atthe electrode, and the transfer coefficient of the reaction.

Shown below in FIGS. 15A-F are the simulations overlaid with theirrespective experimental voltammograms. Note that the very lowconcentrations have a very poor fit, which is likely due to the pooroverall electroactivity of these films. The simulation parameters usedfor these fits are shown in Table 4. The low k_(o) values are possiblydue the distance separation from the FTO substrate to the ferrocenemoieties, since the pendants are located at the center of each linkerand a monolayer of linkers was used to start the growth of these MOFs.These simulated diffusion coefficients are plotted alongside thoseobtained from Anson plots and from redox polymer theory in FIG. 16.

FIGS. 15A, 15B, 15C, 15D, 15E, and 15 F are examples according tovarious embodiments illustrating overlaid simulated and experimentalcyclic voltammograms of Fc MOFs. Table 4 shows parameters of MOFsExtracted from DigiElch Simulation.

TABLE 4 Sample D_(O) (cm² s⁻¹) D_(R) (cm² s⁻¹) α k^(o) (cm s⁻¹) 100% Fc1.4 × 10⁻⁹  2.3 × 10⁻⁹   0.75 3 × 10⁻⁶ 80% Fc 1.4 × 10⁻⁹  1.2 × 10⁻⁹  0.8 4 × 10⁻⁶ 60% Fc 2.1 × 10⁻⁹  3 × 10⁻⁹  0.75 3 × 10⁻⁶ 40% Fc 2.6 ×10⁻¹⁰ 5 × 10⁻¹⁰ 0.6 4 × 10⁻⁶ 20% Fc 3.9 × 10⁻¹¹ 6 × 10⁻¹¹ 0.8 4 × 10⁻⁷10% Fc 5.8 × 10⁻¹¹ 8 × 10⁻¹¹ 0.65 8 × 10⁻⁸

Diffusion Coefficient Theory

In order to better understand the results of how the electroactivity(i.e. peak currents and diffusion coefficients) of the MOFs varied withferrocene content, electron diffusion theory for electroactive polymers,developed by Fritsch-Faules and Faulkner, was used to model thediffusion coefficients of charge in the films. Since the ferrocenewithin the MOFs is spatially fixed, the diffusion coefficients ofoxidized or reduced species are indicators of charge diffusion withinthe film via electron hopping between pendants. The model assumes thatthe redox species are randomly distributed throughout the framework, andthat charge diffusion is controlled by the speed of electron exchangebetween nearest redox neighbors. This rate of electron transfer isexponentially dependent on the distance between neighboring redoxpendants. The diffusion coefficient is given by the following equation:

$D_{E} = \frac{k_{et}r_{NN}^{2}}{6}$

where D_(E) is the diffusion coefficient of electrons in the film,k_(et) is the effective charge transfer rate between pendants, andr_(NN) is the average distance between redox pendants. The transferrate, k_(et), is given by the following equation:

k _(et) =k′e ^(−(r) ^(NN) ^(−r) ⁰ ^()/δ)

where k′ is a constant for a given pendant species representing theintrinsic facility of electron transfer, r₀ is the contact radius (alsomolecular diameter of the pendant: 0.6 nm for ferrocene), and δ is aconstant for the medium denoting the distance dependence of electroniccoupling.

Ferrocene content in the film effects r_(NN), giving a concentrationdependence on the diffusion coefficient of electrons in the film. Theequation for r_(NN) is as follows:

$r_{NN} = {\left( \frac{3}{4\pi \; c} \right)^{1\text{/}3}{e^{\gamma}\left\lbrack {{\Gamma \left( \frac{4}{3} \right)} - {\sum\limits_{n = 1}^{\infty}\; \frac{\left( {- 1} \right)^{n}\gamma^{({n + \frac{4}{3}})}}{{n!}\left( {n + \frac{4}{3}} \right)}}} \right\rbrack}}$

where c is the number concentration of redox pendants (calculated bymultiplying the concentration in mM by Avogadro's number), γ is adimensionless parameter that relates concentration of pendants to anexcluded volume resulting from packing finitely sized pendants(γ=(4/3)πr₀ ³c), and Γ is the gamma function. The summation expressionquickly approaches zero as n increases due to the factorial expressionin the denominator, so the equation easily converges to a real number.

Thus, D_(e) can be modeled as a function of concentration; this functionincreases exponentially at low concentrations, eventually becominglinear before leveling off. The data seems to follow this trend as seenin FIG. 2b in the main text. If experimental diffusion coefficients areknown through experiment, these curves can be fitted to find k′ and δ.Theoretical diffusion coefficients are plotted below in FIG. S13,alongside those found experimentally from Anson plots and those fromDigiElch simulation software fitting.

One factor that is neglected in this theory is the relativeease/difficulty of counter-ion insertion, which is one possible cause ofthe differing D_(O) and D_(R) values for the MOFs. Palmer andcoworkers₂₁ saw the same effect of different diffusion coefficients forfilm oxidation and reduction and suggested the differences may be aresult of counter-ion insertion/expulsion dynamics.

FIG. 16 is an example according to various embodiments illustratingDiffusion coefficients of Fc MOFs determined by Anson plots, simulation,and redox polymer theory. Table 5 shows tabulated diffusion coefficientsfrom different methods.

TABLE 5 D_(E), Redox- D_(R), D_(O), Polymer D_(R), D_(O), DigiElchDigiElch Theory Anson Anson Simulation Simulation (10⁻¹¹ (10⁻¹¹ (10⁻¹¹(10⁻¹¹ (10⁻¹¹ Sample cm² s⁻¹) cm² s⁻¹) cm² s⁻¹) cm² s⁻¹) cm² s⁻¹) 100%Fc 228 230 ± 50)  170 ± 100 160 ± 60  170 ± 40  80% Fc 184 190 ± 9  210± 30  120 ± 20  140 ± 10  60% Fc 134 130 ± 40  150 ± 30  60 ± 10 70 ± 1040% Fc 76.4 650 ± 150 66 ± 10 30 ± 20 27 ± 3  20% Fc 20.9 24 ± 10 21 ±11 13 ± 9  12 ± 10 10% Fc 3.35 6.9 ± 3.7 15 ± 12 3.4 ± 4.0 2.7 ± 2.7

Determination of Redox Conductivity

The redox conductivity of the MOFs can be determined from the diffusioncoefficient and the concentration of Fc using the Einstein-Nernstequation:

σ=λ_(e) ^(o)[Fc]

where:

$\lambda_{e}^{o} = {{\frac{F^{2}}{RT}{D_{e}\lbrack{Fc}\rbrack}} = {x\lbrack{links}\rbrack}_{\max}}$x = fraction  mol  of  Fc  links  from  Zr₆O₆[(Fc)_(x)(NR)_(1 − x)]₆

and:

$\lbrack{links}\rbrack_{\max} = {{\frac{{links}\mspace{14mu} {per}\mspace{14mu} {unit}\mspace{14mu} {cell}}{{crystallographic}\mspace{14mu} {u.c.\mspace{14mu} {volume}}}\lbrack{links}\rbrack}_{\max} = {{\frac{48\mspace{14mu} {links}}{63414.7\mspace{14mu} Å^{3}}\left( \frac{{10^{30}Å^{3}}\mspace{14mu}}{1\mspace{14mu} m^{3}} \right){\left( \frac{1\mspace{14mu} {mol}}{6.024 \times 10^{23}\mspace{14mu} {links}} \right)\lbrack{links}\rbrack}_{\max}} = {{1.26 \times 10^{3}\mspace{14mu} {mol}\mspace{14mu} m^{- 3}} = {1.26\mspace{14mu} M}}}}$

Then, the upper limit of conductivity is:

σ(x=1.0)=1.10 mS m⁻¹

Optical Profilometry Images of MOF Thin-Films

FIG. 17A is an example according to various embodiments illustratingOptical image of 10% Fc thin film. FIG. 17B is an example according tovarious embodiments illustrating Optical image of 20% Fc thin film. FIG.17C is an example according to various embodiments illustrating Opticalimage of 40% Fc thin film. FIG. 17D is an example according to variousembodiments illustrating Optical image of 60% Fc thin film. FIG. 17E isan example according to various embodiments illustrating Optical imageof 80% Fc thin film. FIG. 17F is an example according to variousembodiments illustrating Optical image of 100% Fc thin film.

Gas Adsorption

FIG. 18A is an example according to various embodiments illustrating 50%Fc nitrogen adsorption isotherm at 77 K. FIG. 18B is an exampleaccording to various embodiments illustrating 50% Fc in a Rouquerolplot. FIG. 18C is an example according to various embodimentsillustrating 50% Fc in a BET plot. FIG. 19A is an example according tovarious embodiments illustrating 100% Fc nitrogen adsorption isotherm at77 K. FIG. 19B is an example according to various embodimentsillustrating a Rouquerol plot of a 100% Fc sample. FIG. 19C is anexample according to various embodiments illustrating a BET plot of a100% Fc sample. Table 6 shows BET surface areas for various samples.

TABLE 6 Sample Surface Areas (m² g⁻¹) 0% Fc 1922 ± 46 50% Fc 1652 ± 35100% Fc 1331 ± 15

FIG. 20 is an example according to various embodiments illustratingLinear isotherms of three solid-solutions exhibiting the mesopore tomicropore transition in the inset. FIG. 21 is an example according tovarious embodiments illustrating Pore size distributions of Fc MOFs.

Stability Studies

FIG. 22 is an example according to various embodiments illustrating 50%Fc water adsorption isotherm. FIG. 23 is an example according to variousembodiments illustrating 100% Fc water adsorption isotherm. Table 7shows BET surface areas of samples after water adsorption isotherms.

TABLE 7 Surface Area - Before Surface Area - After Percent Sample (m²g⁻¹) (m² g⁻¹) Decrease 50% Fc 1652 ± 35 1649 ± 35 0.2% 100% Fc 1331 ± 151327 ± 15 0.3%

FIG. 24A is an example according to various embodiments illustrating aPXRD of Fc MOFs having the formula Zr₆O₄(OH)₄[(Fc)₀(NR)₁]₆ before andafter water adsorption isotherms. FIG. 24B is an example according tovarious embodiments illustrating a PXRD of Fc MOFs having the formulaZr₆O₄(OH)₄[(Fc)_(0.5)(NR)_(0.5)]₆ before and after water adsorptionisotherms. FIG. 24C is an example according to various embodimentsillustrating a PXRD of Fc MOFs having the formulaZr₆O₄(OH)₄[(Fc)₁(NR)₀]₆ before and after water adsorption isotherms.

FIG. 25 is an example according to various embodiments illustrating 100%Fc MOF voltammogram in 0.1 M sulfuric acid medium run for 1500 cycles(scan rate: 50 mV s⁻¹). FIG. 26 is an example according to variousembodiments illustrating 100% Fc PXRD before (bottom) and after (top)1500 0.1 M sulfuric acid medium electrochemical cycles (*=FTO). Notethat the only major difference in diffraction is a decrease in theintensity of the 111 peak.

Thermogravimetric Analysis

FIGS. 27A, 27B, 27C, 27D, 27E, 27F, and 27G are examples according tovarious embodiments illustrating TGA of Fc MOFs (blue line is linear,orange line is first derivative).

Infrared Spectroscopy

FIG. 28 is an example according to various embodiments illustrating FTIRof Fc MOFs.

What is claimed is:
 1. A method for producing a metal-organic framework(MOF) having a desired redox conductivity and comprising redox-activelinkers, each having ω-alkyl-ferrocene groups, the method comprising:performing a de novo solvothermal synthesis of the MOF, using theredox-active linkers and redox-inactive linkers in a ratio sufficient toprovide the MOF with the desired redox conductivity.
 2. The methodaccording to claim 1, wherein the MOF displays a maximum electronconductivity of about 122 mS cm⁻¹.
 3. The method according to claim 1,wherein the MOF displays crystallographic and electrochemical stabilityupon a number of redox cycles greater than 1,000.
 4. A metal-organicframework (MOF) linker comprising an ω-alkyl-ferrocene group.
 5. Themetal-organic framework (MOF) linker according to claim 4, having astructure according to Formula I:

wherein R is a C₁ to C₂₄ alkyl.
 6. The metal organic framework (MOF)linker according to claim 5, wherein R is branched.
 7. The metal organicframework (MOF) linker according to claim 5, wherein R is cyclic.
 8. Themetal organic framework (MOF) linker according to claim 5, wherein R islinear.
 9. The metal organic framework (MOF) linker according to claim5, wherein the structure according to Formula I is:


10. A metal-organic framework (MOF), comprising a first plurality ofredox-active linkers, each having an ω-alkyl-ferrocene group.
 11. TheMOF according to claim 10, further comprising one or more redox-inactivelinkers.
 12. The MOF according to claim 11, comprising a repeating unithaving a composition according to Formula II:Zr₆O₄(OH)₄[Fc_(x)NR_(1-x)]₆  (II), wherein Fc represents the pluralityof redox-active linkers, wherein NR represents the one or moreredox-inactive linkers, and wherein x is from 2 to
 100. 13. The MOFaccording to claim 11, wherein the MOF displays a maximum electronconductivity of about 122 mS cm⁻¹.
 14. The MOF according to claim 11,wherein the MOF displays crystallographic and electrochemical stabilityupon a number of redox cycles greater than 1,000.
 15. A thin-filmcomprising the MOF according to claim 10, wherein the thin-film has athickness of from about 5 to about 7 μm.
 16. A bulk powder comprisingthe MOF according to claim
 10. 17. An electrode comprising the MOFaccording to claim 10.